1. Field of the Art
The invention relates to method and device for polishing the edge of a work, and more particularly relates to polishing the edge of a work by use of a rubber wheel (RBW=RUBBER BONDED WHEEL) containing abrasives, instead of using the slurry containing diamond particles for abrasives which may obstruct the tubes of the device and adversely affect the electromagnetic valves and further may be easily congealed at various places, wherein the heat produced by polishing operation is cooled down by air or water, thereby to maintain the quality of the polished work and further to significantly reduce the production cost as well as the running cost of the device.
2. Prior Art
The wafers such as silicon wafers are generally referred to the thin disk-shaped semiconductor elements, and are normally cut out from a refined cylindrical single crystal mother material. The wafer is polished on one side thereof just like a mirror surface and then the surface is provided with various semiconductor elements by way of etching. Further the wafer is required to have the peripheral edge thereof trimmed by way of the emery wheel of diamond and is then polished just like a mirror surface by way of the buff polishing wheel using the slurry, thereby to prevent the dusts from sticking to the surface of the peripheral edge.
Since the conventional polishing wheel is poor in the polishing ability by itself, the slurry containing diamond particles is used to polish the wafer utilizing the chemical etching effect of the slurry which is alkaline. The slurry is a gel which is a mixture of fine abrasive particles of diamond and an alkaline solution (about pH 11).
In case the slurry is used to polish a work, it is necessarily required to provide a solution having the silicon abrasive particles mixed into the slurry. The conventional polishing machine is provided with a separator which is used to separate the abrasive particles from the used slurry after this is recovered, so as to repeatedly use the slurry. The used slurry is, therefore, sent to the tank of the separator through the tubes and the electromagnetic valves. Such a slurry has a nature of hardening and sticking to the objects when it is retained in the tubes and the tank for a long period of time. This will obstruct the tubes and adversely affect the electromagnetic valves.
This is the reason that the slurry is often called as xe2x80x9ca devil waterxe2x80x9d. In order to avoid the obstruction of the tubes, it is required to design the series of tubes to have a flushing structure so as to enable the series of tubes to be washed away of the slurry immediately after the slurry has passed the tubes. Further the metal portions of the device including iron which contact the slurry is required to be the expensive stainless steel coated with Teflon having a thickness of about 0.1 mm so as to avoid the corrosion due to the slurry and also to prevent the slurry from sticking to the portions. Further the tubes must be the Teflon tubes which may be expensive 7 to 10 times as much as the ordinary vinyl tubes. Thus the conventional polishing machine is considerably expensive in the production cost as well as in the running cost.
Further, in case of polishing by use of the slurry, it is required to settle the slurry in the tank bath after the polishing operation to remove the slurry from the solution by washing by way of supersonic waves and then to proceed to the subsequent process. This will considerably reduce the operation efficiency in addition to the probability of adverse influence of the slurry etching upon the wafer. Therefore, it has long been desired to realize the method for polishing the work without using the slurry.
On the other hand, if a rubber wheel containing abrasives is employed instead of the buff wheel, the rubber wheel will be rapidly abraded because the rubber wheel can not yieldingly traverse with respect to the work. Further the rubber wheel will damage the work such as the wafer because the rubber wheel is not so soft as the buff wheel. It is, therefore, required to provide some compensation for the hard rubber wheel to suitably polish the work such as the wafer.
The invention has been provided to eliminate the defects and disadvantages of the prior art. It is, therefore, a principal object of the invention to rotate a rubber wheel containing abrasives in a plane normal to the surface of a thin disk-shaped work and to press the rubber wheel against the peripheral edge of the work without using slurry while using air or water to cool down the heat which is produced during polishing operation.
It is another object of the invention to provide a work edge polishing device significantly inexpensive in the production cost as well as in the running cost, for example, xc2xd to {fraction (1/10)} compared with the conventional device.
It is another object of the invention to provide a plurality of rubber wheels of different polishing abilities which may be occasionally interchanged to polish a specifically hard work in step by step.
It is another object of the invention to provide a rubber wheel having an outer periphery adapted to elastically engage the peripheral edge of the semiconductor wafer so as to polish the edge in a shape of arc.
It is another object of the invention to yielingly move one of the rubber wheel and the work to and from the other during polishing operation so as to moderate the polishing force eliminating the risk of strain or crack which may otherwise be caused in the work.
It is still another object of the invention to provide an adjusting means for adjusting the yielding amount of one of the rubber wheel and the work to and from the other during polishing operation in dependence upon the material of the work to be polished.
In short, the invention substantially comprises disclosed, a rubber wheel containing abrasives and being rotated in a plane normal to a surface of a disk shaped work having a peripheral edge to be polished, a spindle portion holding the rubber wheel such that the rubber wheel may be rotated in a plane normal to the surface of the work, a mount portion for mounting the work thereon such that the work may be movable straight with respect to the rubber wheel in a plane normal to the plane in which the rubber wheel is rotated, elastic means for urging at least one of the spindle portion and the work mounting portion in a direction wherein the rubber wheel and the edge of the work contact with each other, wherein one of the spindle portion and the mount portion is movable toward and away from the other during polishing operation.